冀东高板河锌、硫铁矿矿床中的微生物蓆与矿床成因

MICROBIAL MATS IN THE GAOBANHE ZINC-PYRITE DEPOSIT,EASTERN HEBEI,AND THE GENESIS OF THE DEPOSIT

冀东高板河锌、硫铁矿矿床容矿岩石具有热水沉积岩的地球化学特点。而沿特定层位、一定的岩性分布的层状矿体,也证明该矿床具有热水沉积成因。作者在近年的工作中,于高板河矿床的硫铁矿层中,发现呈蓆状产出的黄铁矿细球菌。丰富多彩的生物结构从一个侧面证实了该矿床中存在生物成矿作用。因此,高板河锌、硫铁矿床是海底热水沉积和微生物成矿双重作用的结果。

The Gaobanhe ore deposit is a well-known zinc-pyrite dpeosit on the northern margin of the North China platform and within the Yanliao metallogenic belt,and the host rocks are sedimentary rocks of Proterozoic Gaoyuzhuang Formation,consisting of manganiferous dolomite,carbonaceous dolomite,siliceous dolomite,siliceous mudstone,manganiferous carbonaceous shale and siliceous banded dolomite.Orebodies layered in form occur along the strata and exhibit gradual relationship with wall rocks. Detailed chemical analyses show that host rocks are characterized by Fe/Ti and(Fe+ Mn)/Ti>20,Al(Al+Fe+Mn)<0.35,and high content of organic carbon,thus exhibiting chemical properties of hot-water sedimentary rocks.Main host rocks are analogous to ores in such REE geochemical features as low ΣREE,high LREE/HREE,positive Eu anomalies and negative Ce anomalies,also quite similar to characteristics of hot water sedimentary rocks. As for pyrite,Co/Ni ratios are mostly lower than 1,S/Se ratios are in the range of 17448～ 306476,and decrepitation temperatures are 296～330℃.Na^+/K^+ of fluid inclusions in sphalerite is as high as 13.75.Fluid salinity calculated from fluid inclusion composition is 29 wt% NaCl.These data demonstrate that the ore deposit is of hot brine sedimentation origin. Quite a lot of microbial textures were found in ores of stratiform orebodies.Pyrite cocci in the form of mats are distributed in the intercalations of ore beds——carbonaceous shale. These pyrite microspherolites might be grouped into four types:Pyrite cocci with wrapped saccate bodies;micelles of pyrite bacteria;pyrite bacilli;pyrite strawberries.It is concluded that the Gaobanhe ore deposit is characterized by dual origin of seawater spouting and bio- genic mineralization.